The present invention is directed generally to a spectrophotometer, and more particularly, to a cell positioner for controlling the position of a movable sample holder for holding a plurality of sample cells in a sample chamber.
A typical arrangement of a prior art cell positioner is that, as depicted in FIG. 3, a position detector composed of a photointerrupter 5 and a position detecting plate 6 is mounted on a driving system ( a unit for transferring power given from a driving motor 7) of the sample cell holder 1, whereby positions of sample cells 2 are detected and controlled under control of an open loop in which an interval L between the sample cells is a known factor with a point, serving as an origin, at which the position detecting plate 6 shields a flux of light of the photointerrupter 5.
The prior art cell positioner, however, presents the following problems. It is required that a position to mount the position detector (including the photointerrupter and the position detecting plate) be accurately adjusted in a moving direction of the sample cell holder in order to direct measurement light of a spectrophotometer spot-on to the center of the sample cell. This adjustment has to be carried out while confirming a stop position of the sample cell holder and a light measuring position, which requires a readjustment for every unit depending on a scatter within an adjusted error range in the optical system of the spectrophotometer as well as being troublesome.